1. Field of the Invention
The invention generally relates to a valve characteristic controller that is used for an internal combustion engine having a variable valve timing mechanism and a variable valve operating angle mechanism. More particularly, the invention relates to improvement in a control for improving fuel efficiency in a low load operation.
2. Description of the Related Art
Variable valve characteristic mechanisms for changing characteristics of engine valves (intake and exhaust valves) have been practically used in internal combustion engines such as on-board internal combustion engines (e.g., Japanese Laid-Open Patent Publication No. JP 2001-263015 A). Examples of the variable valve characteristic mechanisms are a variable valve timing mechanism and a variable operating angle mechanism. The variable valve timing mechanism changes valve timing of engine valves. The variable operating angle mechanism changes an operating angle of engine valves, that is, a crank angle between opening and closing of the engine valves.
Internal combustion engines using both the variable valve timing mechanism and the variable operating angle mechanism for the intake valve have also been practically used. In such internal combustion engines, the valve timing and the operating angle of the intake valve can be independently adjusted according to the operating state of the internal combustion engine. Therefore, valve characteristics can be controlled in a more detailed manner. As a result, fuel consumption capability and exhaust capability of the internal combustion engines can be significantly improved.